Uranium-arsenic oxidation catalysts

ABSTRACT

Catalysts are provided which are useful in the oxidation of olefins to aldehydes and conjugated dienes and in ammoxidation of olefins to nitriles. The catalysts comprise the combined oxides of uranium and arsenic on a catalyst support and the combined oxides of uranium and arsenic promoted by molybdenum, boron, vanadium, tin, nickel, bismuth, chromium, iron, manganese, zinc, tungsten, antimony, cerium, cobalt or rhenium.

United States Patent Grasselli et al. May 30, 1972 [54] URANIUM-ARSENIC OXIDATION [56] References Clted TALYSTS CA UNITED STATES PATENTS K. rasse l ts- [72] Invent 5 12: S f gfg ig fig g 3,542,842 11 1970 Grasselli et a]. ..2oo/4o5.3 Ohio 3,544,616 12/1970 Grasselli et al. ..260/465.3

[73] Assignee: The Standard Oil Company, Cleveland, Primar Examiner-Paul M. Coughlan, Jr.

Ohio Attorney-John F. Jones and Sherman J. Kemmer [22] Filed: Mar. 5, 1970 ABSTRACT [21] Appl' Catalysts are provided which are useful in the oxidation of Related Application Data olefins to aldehydes and conjugated dienes and in ammoxidation of olefins to mmles. The catalysts compnse the combmed commuanon of 691,992, 20, 1967 oxides of uranium and arsenic on a catalyst support and the abandoned combined oxides of uranium and arsenic promoted by molybdenum, boron, vanadium, tin, nickel, bismuth, chromium, [52] U.S. Cl. ..260/680 E, 260/666 A, 260/668 D iron, manganese, zincy tungsten antimony, cerium, b l or [5 l Int. Cl ..C07c 5/18 rhenium [58] Field of Search ..260/68O E 9 Claims, No Drawings URANIUM-ARSENIC OXIDATION CATALYSTS CROSS REFERENCE TO RELATED APPLICATIONS This is a continuation of US. Pat. application, Ser. No. 691,992 filed Dec. 20, 1967 now US. Pat. No. 3,544,616.

BACKGROUND OF THE INVENTION This invention relates to oxidation catalysts comprising oxides of uranium and arsenic optionally incorporating promoters, which are useful for the catalytic oxidationof olefins to aldehydes and conjugated dienes, and for the catalytic ammoxidation of olefins to nitriles. The catalytic oxidation reactions are exemplified by the oxidation of propylene to acrolein, the oxidation of isobutylene to methacrolein, the oxydehydrogenation of an olefin having 4 to 8 carbons, such as the oxydehydrogenation of butene-l or butene-2 to butadiene-l,3, the ammoxidation of propylene to acrylonitrile and the ammoxidation of isobutylene to methacrylonitrile.

The prior art is replete with a multiplicity of oxidation catalysts particularly suited to the same reactions disclosed herein. Some of these oxidation catalysts are disclosed in U.S. Pats. Nos. 2,904,580; 3,142,697; 3,179,694; 3,197,419; 3,198,750; 3,200,081; 3,200,084; 3,226,421; 3,248,340; 3,264,225; 3,251,900; 3,257,474; 3,260,768; French Pats. Nos. 1,255,121; 2,269,382; and British Pats. Nos. 864,666; 876,446; 983,755. It is well-known that some catalysts are more successful than others and that the search for economically competitive catalysts continues unremittingly. The oxidation catalyst of the instant invention is a superior catalyst.

DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION The uranium oxide-arsenic oxide base catalyst disclosed herein is referred to as a mixture of uranium and arsenic oxides, but this is not to be construed as meaning that the catalyst is composed either in whole or in part of only these compounds. The proportions of arsenic and uranium in the catalyst system may vary widely. The preferred uraniumzarsenic atomic ratio ranges from about 25:1 to about 1:6; optimum activity appears to be obtained at uranium:arsenic atomic ratios within the range of from about 1:1 to about 1:4 and the catalyst is characterized by a negligible loss of arsenic despite the relatively high reaction temperatures of the catalytic processes in which it is useful.

The catalyst of the instant invention contains from to 95 percent by weight of a catalyst support, and preferably between 10 percent and 90 percent. Any known catalyst support such as alumina, pumice, silicon carbide, titania, zirconia, alumina-silica, and the inorganic phosphates, silicates, aluminates, borates and carbonates stable under the reaction conditions, may be used but silica is preferred.

In the preparation of the base catalyst useful in this invention, the arsenic oxide and uranium oxide can be blended together or can be formed separately and then blended or formed separately, or together in situ.

The uranium oxide component of the instant catalyst can be useful in the form of uranous, uranic or combined uranousuranic oxides, or by precipitation in situ from a soluble uranyl salt, such as the nitrate, acetate, or a halide such as the chloride. Uranium metal can be used as a starting material, and if free arsenic is also employed, the arsenic can be converted to the oxide and the uranium to the nitrate simultaneously by oxidation in hot nitric acid. A slurry of hydrous arsenic-arsenic oxide in nitric acid can be combined with a solution of a uranium salt which is then precipitated in situ as the hydroxide by making the solution alkaline with ammonium hydroxide, the ammonium nitrate and the other ammonium salts being removed by filtration of the resulting slurry or by thermal decomposition.

It will be apparent from the above that uranous and uranic bromides, chlorides, fluorides and iodides, nitrates, acetates, sulfites, sulfates, phosphates, thiocyanates, thiosulfates, oxalates, formates and hydroxides can be employed as the source of the uranium oxide components. A preferred source is uranyl nitrate.

As starting materials for the arsenic oxide component there can be used any arsenic oxide such as arsenic trioxide or arsenic pentoxide; or a hydrolyzable or decomposable arsenic salt such as an arsenic halide. Arsenic metal can be employed, the oxide being formed by oxidizing the metal with an oxidizing acid, such as nitric acid. A preferred starting material is ortho-arsenlc acid. v

The catalytic activity of the novel catalyst embodied in the present invention, is enhanced by heating the catalyst at an elevated temperature. Preferably, the catalyst mixture is dried and heated at a temperature of from 500 to 1,500 F, more preferably at about 700 F to 900 F for from 2 to 24 hours. If activity then is insufficient, the catalyst can be further heated at a temperature above about 1,000" F but below a temperature deleterious to the catalyst at which it is melted or decomposed, preferably from about l,l00 to about 1,800 F for from 1 to 48 hours, in the presence of oxygen or an oxygencontaining gas such as air.

In general the higher the activation temperature, the less time required to effect activation. The sufficiency of activation at any given set of conditions is ascertained by a spot test of a sample of the material for catalytic activity. Activation is best carried out in an open chamber, permitting circulation of air or oxygen, so that any oxygen consumed will be replaced.

The instant catalyst comprising the combined oxides of uranium and arsenic may be defined by the following empirical formula U, As, 0, where the As:U atomic ratio is in the range from about 1:25 to about 10:1 and z is determined by the oxidation state of U and As in the catalyst. It is conjectured that the combined oxides of the instant catalyst are present as an activated catalytic oxide complex.

Various metal oxides have been found to act as promoters in conjunction with the uranium-arsenic base catalyst, as for example, minor amounts of an element or elements selected from Groups l-A, l-B, ll-A, lI-B, Ill-B, IV-A, IVB, V-B, VI-B, VII-B, and VIII of the Periodic Table. Particularly effective promoters are the oxides of molybdenum, boron, vanadium, tin, nickel, bismuth, chromium, iron, manganese, zinc, antimony, cerium, and tungsten in an amount corresponding to less than one atomic equivalent per atomic equivalent of either uranium or arsenic.

Promoter oxides may be incorporated into the base catalyst by blending into the gel before calcining, or by blending into the oven-dried base catalyst before calcining. A preferred manner of incorporating promoter elements is by choosing a water-soluble salt of the promoter element, forming an aqueous solution of the salt, and mixing this solution with uranyl nitrate and ortho-arsenic acid solutions, and stirring while continuously heating till the solution gels. The gel is then spooned into trays and oven-dried at C overnight. The dried catalyst is then calcined starting at 800 F, the temperature raised to 900 F over a period of 2 hours and the catalyst calcined overnight at this temperature. A further calcination at a higher temperature of at least l,000 F for 3 hours is generally employed to increase the activity of the catalyst complex. This catalyst system is useful in the oxidation of olefins to oxygenated compounds, such as aldehydes and acids, in the presence of oxygen; in the oxidation of olefins to unsaturated nitriles in the presence of oxygen and ammonia; and in the oxydehydrogenation of olefins to diolefins and aromatic compounds. Nitriles and oxygenated compounds such as aldehydes and acids can be produced simultaneously using process conditions within the overlapping ranges for these reactions as set forth in detail below. The relative proportions of each that are obtainable will depend on the process conditions, the particular catalyst and on the olefin. The same catalyst may produce predominantly the nitrile with propylene and predominantly the aldehyde and/or acid with isobutylene. The term oxidation as used in this specification and claims encompasses the oxidation to aldehydes and acids and to nitriles and dienes all of which oxidation reactions require oxygen as a reactant.

OXIDATION OF OLEFINS TO ALDEHYDES AND ACIDS The reactants used in the oxidation to oxygenated compounds are oxygen and an olefin having only three carbon atoms in a straight chain such as propylene or isobutylene or mixtures thereof.

The olefins may be in admixture with paraffinic hydrocarbons, such as ethane, propane, butane, and pentane; for example, a propylene-propane mixture may constitute the feed. This makes it possible to use ordinary refinery streams without special preparation.

The temperature at which this oxidation is conducted may vary considerably depending upon the catalyst, the particular olefin being oxidized and the correlated conditions of the rate of throughput or contact time and the ratio of olefin to oxygen. In general, when operating at pressures near atmospheric, i.e., l to 100 psig, temperatures in the range of 500 to 1,100 F may be advantageously employed. However, the process may be conducted at other pressures, and in the case where superatmospheric pressures, e.g., above 100 psig, are employed, somewhat lower temperatures are possible. In the case where this process is employed to convert propylene to acrolein, a temperature range of 750 to 950 F has been found to be optimum at atmospheric pressure.

While pressures other than atmospheric may be employed, it is generally preferred to operate at or near atmospheric pressure, since the reaction proceeds well at such pressures and the use of expensive high pressure equipment is avoided.

The apparent contact time employed in the process is not critical and it may be selected from a broad operable range which may vary from 0.1 to 50 seconds. The apparent contact time may be defined as the length of time in seconds which the unit volume of gas measured under the conditions of reaction is in contact with the apparent unit volume of the catalyst. It may be calculated, for example, from the apparent volume of the catalyst bed, the average temperature and pressure of the reactor, and the flow rates of the several components of the reaction mixture.

The optimum contact time will, of course, vary depending upon the olefin being treated, but in the case of propylene and isobutylene, the preferred apparent contact time is 0.15 to seconds.

A molar ratio of oxygen to olefin between about 0.5:] to 5:1 generally gives the most satisfactory results. For the conversion of propylene to acrolein, a preferred ratio of oxygen to olefin is from about 1:1 to about 2: 1. The oxygen used in the process may be derived from any source; however, air is the least expensive source of oxygen and is preferred. for that reason.

Water is formed as a product of reaction and it has been found that it has a beneficial influence on the course of the reaction in that it improves the conversion and the yields of the desired product. Sometimes it is desirable to add some water to the reaction mixture. The manner in which water affects the reaction is not fully understood but the theory of this phenomenon is not deemed important in view of the experimental results we have obtained.

Inert diluents, such as nitrogen and carbon dioxide, may be present in the reaction mixture.

OXIDATION OF OLEF INS TO NITRILES The reactants are the same as those used in the oxidation of olefins to aldehydes described above except that ammonia is included as a reactant. Any of the olefins described above can be used.

In its preferred aspect, the process comprises contacting a results. The molar ratio of oxygen to the olefin in the feed to the reaction vessel should be in the range of 0.5:1 to 4:1 and a ratio of about 1:1 to 3:1 is preferred.

Low molecular weight saturated hydrocarbons do not appear to influence the reaction to an appreciable degree, and these materials can be present; consequently the addition of saturated hydrocarbons to the feed to the reaction is contemplated within the scope of this invention. Likewise, diluents, such as nitrogen and the oxides of carbon, may be present in the reaction mixture without deleterious effect.

The molar ratio of ammonia to olefin in the feed to the reactor may vary between about 0.05:1 to 5:1. There is no real upper limit for the ammoniazolefin ratio, but there is generally no reason to exceed the 5:1 ratio. At ammonia:olefin ratios appreciably less than the stoichiometric ratio of 1:1, various amounts 'of oxygenated derivatives of the olefin will be formed.

Significant amounts of unsaturated aldehydes, as well as nitriles, will be obtained at ammoniazolefin ratios substantially below 1:1, i.e., in the range of 0.15:1 to 0.75:1. Outside the upper limit of this range only insignificant amounts of aldehydes will be produced, and only very small amounts of nitriles will be produced at ammonia:olefin ratios below the lower limit of this range. It is fortuitous that within the ammoniazolefin range stated, maximum utilization of ammonia is obtained and this is highly desirable. It is generally possible to recycle any unreacted olefin and unconverted ammonia.

A particularly surprising aspect of this invention is the effect of water on the course of the reaction. We have found that in many cases water in the mixture fed to the reaction vessel improves the selectivity of the reaction and the yield of nitrile. However, reactions not including water in the feed are not to be excluded from this invention inasmuch as water is formed in the course of the reaction.

In general, the molar ratio of added water to olefin, when water is added, is at least about 0.25:1. Ratios on the order of 1:1 to 3:1 are particularly desirable, but higher ratios may be employed, i.e., up to about 10:1.

The reaction is carried out at a temperature within the range of from about 550 to l,lO0 F. The preferred temperature range is from about 800 to 1,000 F.

The pressure at which the reaction is conducted is also an important variable, and the reaction should be carried out at about atmospheric or slightly above atmospheric (2 to 3 atmospheres) pressure. In general, high pressures, i.e., about 250 psig, are not suitable, since higher pressures tend to favor the formation of undesirable by-products.

The apparent contact time is not critical, and contact times in the range of from 0.1 to about 50 seconds may be employed. The optimum contact time will, of course, vary depending upon the olefin being treated, but in general, a contact time of from 1 to 15 seconds is preferred.

THE OXIDATIVE DEHYDROGENA'I'ION OF OLEFINS TO DIOLEFINS AND AROMATICS In accordance with the present invention, the promoted or unpromoted catalyst system is employed in the catalytic oxidative dehydrogenation of olefins to diolefins and aromatic compounds. In the process, the feed stream in vapor form containing the olefin to be dehydrogenated and oxygen is conducted over the promoted catalyst at a comparatively low temperature to obtain the corresponding diolefin or aromatic compound.

By the term olefin as used herein is meant the open chain as well as cyclic olefins. The olefins dehydrogenated in accordance with this invention have at least four and up to about eight non-quaternary carbon atoms, of which at least four are arranged in series in a straight chain or ring. The olefins preferably are either normal straight chain or tertiary olefins. Both cis and trans isomers, where they exist, can be dehydrogenated.

Among the many olefinic compounds which can be dehydrogenated in this way are butene-l; butene-2; pentene- 1; pentene-2; heptene-l; octene-l; tertiary pentenes and hexenes having one tertiary carbon atom such as 2-methyl-pentene-l S-methyI-butenel 3,4-dimethyl-pentene-1, 4-methylpentene-Z; other branched chain olefins such as Z-methyl-butene-2, Z-methyl-butene-l, 3-methyl-pentene-2; cyclo-olefins such as cyclopentene; cyclohexene; 3-methyl cyclohexene and cycloheptene.

Open chain olefins yield diolefins, and, in general, six-membered ring olefins yield aromatic ring compounds. The higher molecular weight open chain olefins may cyclize to aromatic ring compounds.

The feed stock in addition to the olefin and oxygen can contain one or more paraffinic or naphthenic hydrocarbons having up to about carbon atoms, which may be present as impurities in some petroleum hydrocarbon stocks and which may also be dehydrogenated in some cases. In this oxidative dehydrogenation reaction, propylene and isobutylene should not be included in the feed in substantial amounts.

The amount of oxygen should be within the range of from about 0.3 to about 3 moles per mole of olefin. Stoichiometrically, 0.5 to 1.5 moles of oxygen per mole of olefin is required for the dehydrogenation to diolefins and aromatics respectively. It is preferred to employ an excess of oxygen, from 1 to about 2 moles per mole of olefin, in order to ensure a higher yield of diolefin per pass. The oxygen can be supplied as pure or substantially pure oxygen or as air or in the form of hydrogen peroxide.

When pure oxygen is used, it may be desirable to incorporate a diluent in the mixture such as steam, carbon dioxide or nitrogen.

The feed stock is preferably catalytically dehydrogenated in the presence of steam, but this is not essential. Usually, from about 0.1 to about 6 moles of steam per mole of olefin reactant is employed, but amounts larger than this can be used.

The dehydrogenation proceeds at temperatures within the range of from about 325 to about 1,000 C. Optimum yields are obtainable at temperatures within the range from about 400 to 550 C. However, since the reaction is exothermic, temperatures in excess of 550 C should not be used, unless means are provided to carry ofi" the heat liberated in the course of the reaction. Due to the exothermic nature of the reaction, the temperature of the gaseous reaction mixture will be higher than the temperature of the feed entering the system by as much as 75 C. The temperatures referred to are those of the entering gas feed near the reactor inlet.

The preferred reaction pressure is approximately atmospheric, within the range of from about 5 to about 75 psig. Higher pressures up to about 300 psig can be used and have the advantage of simplifying the product recovery.

Only a brief contact time with the catalyst is required for effective dehydrogenation. The apparent contact time with the catalyst can vary from about 0.5 up to about 50 seconds but higher contact times can be used if desired. At these contact times, comparatively small reactors and small amounts of catalyst can be used efi'ectively.

In general, any apparatus of the type suitable for carrying out oxidation reactions in the vapor phase may be employed in the execution of these processes. The processes may be conducted either continuously or intermittently. The catalyst bed may be a fixed bed employing a large particulate or pelleted catalyst or, in the alternative, a so-called fluidized" bed of catalyst may be employed.

The reactor may be brought to the reaction temperature before or after the introduction of the reaction feed mixture. However, in a large-scale operation, it is preferred to carry out the process in a continuous manner, and in such a system, the recirculation of the unreacted olefin is contemplated.

The catalyst compositions and oxidation process of this invention are further illustrated in the following examples wherein the amounts of the various ingredients are expressed as parts by weight unless otherwise specified.

EXAMPLES 1-l6 1. In a typical preparation of the unpromoted catalyst, 87.8

g of uranyl nitrate (U0 (NO .6H O were ,dissolved in about cc of hot water; 154.3 g of ortho-arsenic acid H AsO .b& H 0 were dissolved in about 400 cc of hot water.

The uranyl nitrate solution was added to the dilute ortho-arsenic acid and the mixture stirred. To this mixture was added 1 16.8 g of Ludox AS, a commercially available dispersion of 30 percent by weight of silica, SiO The mixture was continuously heated with constant stirring until it gelled. The gel was spooned into trays, placed in an atmospheric convection oven at C and dried overnight. The oven-dried catalyst was then heat-treated in a furnace open to the atmosphere, starting at 800 F and being raised to 900 F over a period of about two hours. The catalyst was calcined overnight at 900 F. The catalyst obtained had a composition which may be written as 82.5% UAS,,, ,O,-,,, 17.5% SiO;.

2. A portion of the above-described catalyst (calcined at 900 F) was further calcined at l,200 F for 3.5 hours.

3. A portion of the above-described catalyst (calcined at 900 F) was further calcined at 1,375 F for 3 hours.

4. In another preparation of the unpromoted catalyst, 215 g of uranyl nitrate were dissolved in about 200 cc of hot water; 64.6 g of ortho-arsenic acid H AsO H O were dissolved in about 100 cc of hot water. The uranyl nitrate solution was added to the dilute ortho-arsenic acid and the mixture stirred. To this mixture was added 116.8 g of Ludox AS a commercially available dispersion of 30 percent by weight of silica, SiO The mixture was continuously heated with constant stirring until it gelled. The gel was spooned into trays, placed in an atmospheric convection oven at 120 C and dried overnight. The oven-dried catalyst was then heat-treated in a furnace open to the atmosphere, starting at 800 F and being raised to 900 F over a period of about 2 hours. The catalyst was calcined overnight at 900 F. The catalyst obtained had a composition which may be written as 82.5% UASO5 5 17.5% SiO 5. A portion of the above-described catalyst (calcined at 900 F) was further calcined at 1,200 F for 3.5 hours.

6. A portion of the above-described catalyst (calcined at 900 F) was further calcined at 1,500 F for 3 hours.

7. A portion of the above-described catalyst (calcined at 900 F) was further calcined at 1,700 F for 3 hours.

8. In another preparation of the unpromoted catalyst 239 g of uranyl nitrate (UO )(NO .6H O were dissolved in about 200 cc of hot water; 48.1 g of ortho-arsenic acid H AsO H O were dissolved in about 100 cc of hot water. The uranyl nitrate solution was added to the dilute ortho-arsenic acid and the mixture stirred. To this mixture was added 116.8 g of Ludox AS, a commercially available dispersion of 30 percent by weight of silica, SiO The mixture was continuously heated with constant stirring until it gelled. The gel was spooned into trays, placed in an atmospheric convection oven at 120 C and dried overnight. The oven-dried catalyst was then heat-treated in a furnace open to the atmosphere, starting at 800 F and being raised to 900 F over a period of about 2 hours. The catalyst was calcined overnight at 900 F. The catalyst obtained had a composition which may be written as 9. A portion of the above-described catalyst (calcined at 900 F) was further calcined at l,200 F for 3.25 hours.

10. A portion of the above-described catalyst (calcined at 900 F) was further calcined at 1,500 F for 3.5 hours.

11. A portion of the above-described catalyst (calcined at 900 F) was further calcined at l,750- F for 3 hours.

Other catalyst compositions were prepared in a manner similar to that described hereinabove, so as to vary the ratio of arsenic to uranium. Ratios as low as 0.1 gave good conversions, though the better conversions were obtained with ratios in excess of 2.

The following Table I shows runs for the conversion of propylene to acrylonitrile, made with each of the abovedescribed unpromoted catalysts, all the runs having been made under substantially similar process conditions, namely a weight hourly space velocity (WWI-l) in the range from about 0.04 to about 0.1 hr.", a reactor temperature in the range from about 850 to about 950 F and a slight excess of ammonia over the theoretical amount, at substantially atmospheric pressure,

Percent Conversion Moles Acrylonitrile Recovered X to Acrylonitrile Moles Propylene Fed 100 TABLE l-UNPROMOTED CATALYST Atomic Ratio Calcined Over- Percent Per Pass Ex. Arsenic: night at 900F & Conversion of Propy- No. Uranium Additionally for lene to Acrylonitrile l 5.8 39.6-G 2 5.8 3.5 hrs. at l,200F 59.4

3 5.3 3 hrs. at l,375F 57.3

5 1 3.5 hrs. at l,200F 45.7

6 1 3 hrs. at l,500F 24.9

7 1 3 hrs. at l,700F 18.1

9 0.7 3.25 hrs. at 1,200F 28.4 10 0.7 3.5 hrs. at 1,500F 23.1 1 1 0.7 3 hrs. at 1,700F l 1.5 12 0.2 19.3-0 l3 2 47.6 14 3 3 hrs. at l,OOOF 57.2 15 3 3 hrs. at l,200F 48.3 16 8 39.3-G

The following Table ll shows runs for the conversion of isobutylene to methacrylonitrile, made with some of the above-described unpromoted catalysts, all the runs having been made under substantially similar process conditions as those described for preceding Table I.

TABLE II UNPROMOTED CATALYST Atomic Ratio Calcined Overnight Per Pass Con- Ex. Arsenic: at 900F and version Isobutylene No. Uranium Additionally for to Methacrylonitrile 17 0.7 3 hrs. at 1,500F l9'.8 18 l 3.5 hrs. at l,200F 39.7 19 2 3 hrs. at 1,700F 29.6 20 3 3 hrs. at 1,200F 42.8 21 5.8 3 hrs. at l,375F 57.7

The following Table III shows runs, for the conversion of propylene to acrylonitrile, made with some of the abovedescribed promoted catalysts, all the runs having been made under substantially similar process conditions as those described for preceding Table I. The promoted catalyst composition may be written M, U As 0 where M denotes the promoter element and values for the symbols 0, x and y are listed in the following Table ll I.

28 Nickel 0. l l 3 59.7 29 Tin 0. l l 3 60.1 30 Vanadium 0. l l 3 61 3 1 Boron 0. l l 3 61.1 32 Molybdenum 0.] 1 3 71.9

The following Table IV shows runs, for the conversion of isobutylene to methacrylonitrile, make with some of the above-described promoted catalysts, all the runs having been made under substantially similar process conditions as those described for the preceding Table l. The promoted catalyst composition may be written M. U I As, 0 where M denotes the promoter element and values for the symbols 0, x and y are listed in the following Table IV.

TABLE IV Atomic Calcined Overk Per Pass Ratios of night at 900F Conversion Ex. Componentsand Additionally of Propylene No. Promoter a x y for to Acrolein 33 Molybdenum 1 1 0.25 3 hr. at l,l00F 56.1 34 Antimony l l 3 3 hr. at 1,000F 9.4 35 Vanadium 0.1 1 3 3 hr. at l,OOOF 8.3

The following Table V shows runs, for the conversion of propylene to acrolein, made with some of the above-described unpromoted and promoted catalysts, all the runs having been made under substantially similar process conditions as those described for preceding Table l. The promoted catalyst composition M,, U I As, 0, where M denotes the promoter element and values for the symbols 0, x and y are listed in the following Table V.

TABLE V Atomic Calcined Over- Per Pass Ratios of night at 900F Conversion Ex. Componentsand Additionally of Propylene No. Promoter a x y for to Acrolein 36 None l 0.7 3 hrs. at 1,500F 9.0 37 None l 4.5 3 hrs. at 900F 12.8 38 None l 5.8 3 hrs. at 1,000F 14.9 39 Molybdenum 3 l 0.25 3 hrs. at l,l00F 50.2 40 Iron 0.1 l 3.0 3 hrs. at 1,000F 28.4 41 Vanadium l 1 3.0 3 hrs at 1,200F 37.9 42 Bismuth 1 1 3.0 3 hrs at 1,000F 32.8

The following Table Vl shows runs, for the conversion of isobutylene to methacrolein, made with some of the abovedescribed unpromoted and promoted catalysts, all the runs having been made under substantially similar process conditions as those described for preceding Table l. The promoted catalyst composition may be written M U As O where M denotes the promoter element and values for the symbols a, x and y are listed in Table VI below.

TABLE VI Atomic Calcined Over- Per Pass Ratios of night at 900T Conversion of Ex. Componentsand Additionally isobutylene to No. Promoter a x y for methacrolein 43 None l 0.7 3 hr. at 900F l 1.9 44 None l 4.5 3 hr. at 1,000F 14.7 45 None 1 5 3 hr. at 1,200F 18.8 46 Nickel l 1 3 3 hr. at 1,000F 31.9 47 Tin 0.5 l 3 3 hr. at 1,100F 29.8 48 Molybdenum l 1 3 39.8

The following Table Vll shows runs, for the conversion of lbutene to butadiene, made with some of the above-described promoted catalysts, all the runs having been made under sub stantially similar process conditions as those described under preceding Table I. The promoted catalyst composition may be written M U A5,, 0, where M denotes the promoter element and values for the symbols a, x and y are listed in the Table Vll below.

We claim:

1. The process for the oxidative dehydrogenation of olefins comprising contacting a mixture of oxygen and an olefin having at least four and up to about eight non-quatemary carbon atoms of which at least four are arranged in a straight chain in the vapor phase at a temperature at which the oxidative dehydrogenation proceeds with a promoted catalyst composition consisting essentially of a base catalyst, a support and a promoter component, said base catalyst consisting essentially of oxides of arsenic and uranium, the AszU atomic ratio being within the range of about 6:1 to about l:25, said support being silica and said promoter component consisting essentially of an oxide of at least one element selected from the group consisting of molybdenum, boron, vanadium, tin, nickel, bismuth, chromium, iron, manganese, zinc, tungsten, antimony and cerium.

2. The process in claim 1 wherein the oxidative dehydrogenation reaction is carried out at a temperature within the range of about 400 to 550 C.

3. The process in claim 2 wherein the ratio of oxygen to olefin is within the range of from about 0.3 to 3 moles of oxygen per mole of olefin.

4. The process in claim 3 wherein the reaction pressure is within the range of from about 5 to 75 psig.

5. The process in claim 4 wherein the apparent contact time of the olefin with the catalyst is within the range of about 0.5 to 50 seconds.

6. The process in claim 5 wherein the olefin consists of butene-l.

7. The process in claim 5 wherein the promoter component consists of molybdenum.

8. The process in claim 5 wherein the promoter component consists of vanadium.

9. The process in claim 5 wherein the catalyst composition contains from 10 to percent by weight of the catalyst support. 

2. The process in claim 1 wherein the oxidative dehydrogenation reaction is carried out at a temperature within the range of about 400* to 550* C.
 3. The process in claim 2 wherein the ratio of oxygen to olefin is within the range of from about 0.3 to 3 moles of oxygen per mole of olefin.
 4. The process in claim 3 wherein the reaction pressure is within the range of from about 5 to 75 psig.
 5. The process in claim 4 wherein the apparent contact time of the olefin with the catalyst is within the range of about 0.5 to 50 seconds.
 6. The process in claim 5 wherein the olefin consists of butene-
 7. The process in claim 5 wherein the promoter component consists of molybdenum.
 8. The process in claim 5 wherein the promoter component consists of vanadium.
 9. The process in claim 5 wherein the catalyst composition contains from 10 to 90 percent by weight of the catalyst support. 